The present invention relates to an angular velocity sensor having a self diagnosis function.
A conventional tuning fork type angular velocity sensor has a detecting part comprising detector plates 13 and 14 and a driving part comprising driver plates 11 and 12. As shown in FIG. 19, detector plates 13 and 14 are located at the top of the driver plates 11 and 12, respectively. Each detector plate 13 and 14 is joined orthogonally to a respective driver plate 13 and 14. When an angular velocity is applied to the angular velocity sensor and while keeping the driving part in continuous tuning fork vibration, the angular velocity is detected by the output of the detector plates 13 and 14, which vibrate in opposite directions to each other corresponding to the applied angular velocity.
In an angular velocity sensor in accordance with the prior art, a tightly sealed space is formed by a lid 2, which is made of resin. Lid 2 is attached at an aperture of a case 1, also made of resin, of which one end is open, as shown in FIG. 18.
Inside the tightly sealed space, a circuit board 3 and a metallic weight plate 4 are contained. Supporting pins 5 are attached at four corners inside the case 1, and weight plate 4 and circuit board 3 are elastically supported and fixed by the supporting pins 5. Dampers 6 made of rubber are attached at the four corners of weight plate 4 for the elastic support. Supporting legs 7 made of resin are put between damper 6 and circuit board 3. Supporting pins 5 are compressed at the tips toward the circuit board 3 side after penetrating dampers 6, supporting legs 7 and circuit board 3. Thus, circuit board 3 and weight plate 4 are elastically supported and fixed. A metallic supporting pin 8 is inserted and fixed vertically to weight plate 4, on the circuit board 3 side, as shown in FIG. 19. One end of a metallic supporting pin 9, laid parallel to weight plate 4, is inserted and fixed to supporting pin 8. The diameter of supporting pin 9 is about one fifth of the diameter of supporting pin 8. Furthermore supporting pin 9 is made of metallic material having elasticity, such as a piano wire, wherein the other end of supporting pin 9 is fixed to a metal plate 10 by soldering.
One end of each of metallic driver plates 11 and 12, which are sandwiching supporting pins 8 and 9 therebetween, is fixed to each side of metal plate 10. Plate-shaped piezoelectric elements 11a and 12a are fixed on the surfaces of metallic driver plates 11 and 12, respectively. In this way, the tuning fork type driving part is formed. The other ends of driver plates 11 and 12 are twisted orthogonally relative to piezoelectric elements 11a and 12a to form detector plates 13 and 14. Other plate-shaped piezoelectric elements 13a and 14a are fixed on detector plates 13 and 14, as shown in FIG. 19. In this way, the detecting part is formed. The angular velocity sensor is composed of the driving part and the detecting part.
There is a problem with the conventional angular velocity sensor however. Namely, the conventional sensor has no ability to detect information about the occurrence of a malfunction of the components, nor the ability to send such information, judged to be a malfunction of the components, to the outside (e.g., such that an operator can be notified of the malfunction).
The present invention provides a sensor that allows detection from outside the sensor of a malfunction in the sensor, resulting from partial damage to the sensor, that prevents the sensor from performing accurate angular velocity detection. Accordingly, the present invention provides a highly reliable angular velocity sensor.
To achieve the stated purpose, an angular velocity sensor of the present invention includes (1) a sensor element having a driver part and a detector part for detecting an angular velocity, (2) drive means including a driver circuit for supplying a driving signal to the driving part of the sensor element and a monitor circuit to which a monitor signal is supplied from the sensor element and stably driving and vibrating the driver part of the sensor element by applying the output of the monitor circuit to the driver circuit through an AGC (automatic gain control) circuit, (3) detection means including a charging amplifier to which an output of the detector part of the sensor element is supplied and a synchronous detector to which an output of the charging amplifier is supplied through a band pass filter and detecting an output of the band pass filter synchronizing with a driving signal from the drive means and outputting an angular velocity signal, and (4) self diagnosis means receiving a mechanical coupling signal obtained from the detection means other than an angular velocity signal, detecting abnormality of the sensor element and outputting a self diagnosis signal.
Also, an angular velocity sensor according to another aspect of the present invention includes, (1) a sensor element with a vibrating part and detector part for detecting an angular velocity, (2) drive means including a driver circuit and a monitor circuit similar to that mentioned above, (3) detection means including a pair of current amplifiers, a differential amplifier and a synchronous demodulator, in which the pair of current amplifiers receive outputs from the detector part of said sensor element, the differential amplifier amplifies a difference in outputs from the pair of current amplifiers and in which the synchronous demodulator detects an output from the differential amplifier in synchronous with the driving signal from the drive means and outputs an angular velocity signal, and (4) self diagnosis means for outputting a diagnosis signal to detect an abnormality of the sensor element by coupling a signal synchronized with the driving signal to the synchronous demodulator.
According to the above composition, by making the mechanical coupling signal always obtained from the detection means as a signal for self diagnosis, whether the angular velocity signal is in a state to be detected normally or not can be easily checked. Also as the mechanical coupling signal is always generated, it is unnecessary to independently provide means for generating the mechanical coupling signal. Accordingly, not only is the composition very simple and highly reliable for self diagnosis, but it also makes it possible to know when the characteristics of the sensor become stable after the sensor starts to work so that sensor output information can be utilized at its earliest possible time.